[Kea-users] Global host reservations - unexpected behavior

[Maria Hrabosova]

Hello,

I found a use case in which KEA DHCP server behaves differently than I 
expected and I would like to ask if it was meant to behave that way or 
there is a problem in my configuration. Here is the description:

Imagine you have a known host client-X with a reserved IP address 
10.0.0.9. client-X usually connects via the Shared-B network, but one 
day it wants to connect via Shared-A. The IP address reserved for 
client-X does not match any of the subnets in Shared-A. Therefore, I 
would expect that it would be given an IP address from the pool in the 
subnet 10.1.1.0/24 (that is how it works in ISC DHCP). However, it is 
given it's reserved IP 10.0.0.9 along with the options from the subnet 
10.1.1.0/24, which does not make sense to me. Is this how it was meant 
to behave?

I found a solution how to make the client-X get an IP address from the 
pool in the subnet 10.1.1.0/24 by moving the host reservation from the 
global scope to the scope of the subnet 10.0.0.0/24. Anyway, I've been 
wondering why it doesn't work the same way with the global reservations. 
I tried the global mode first, as I am using host reservations in groups 
(which are global) in ISC DHCP and it works as expected there.

Could you please give it a look? Thanks in advance. See the 
corresponding configuration and the demonstration of the use case below.

Best regards,

Maria Hrabosova


---

kea-dhcp4.conf:

{
   "Dhcp4": {
     "interfaces-config": {
       "interfaces": [
         "server-eth0"
       ],
       "dhcp-socket-type": "udp"
     },
     "control-socket": {
       "socket-type": "unix",
       "socket-name": "/tmp/kea-dhcp4-ctrl.sock"
     },
     "lease-database": {
       "type": "memfile"
     },
     "shared-networks": [
       {
         "name": "Shared-A",
         "relay": {
           "ip-address": "192.0.2.1"
         },
         "subnet4": [
           {
             "subnet": "10.1.1.0/24",
             "pools": [
               {
                 "pool": "10.1.1.200 - 10.1.1.250"
               }
             ],
             "option-data": [
               {
                 "name": "routers",
                 "data": "10.1.1.1"
               },
               {
                 "name": "domain-name-servers",
                 "data": "10.1.1.2, 10.1.1.3"
               }
             ]
           }
         ]
       },
       {
         "name": "Shared-B",
         "relay": {
           "ip-address": "192.0.1.1"
         },
         "subnet4": [
           {
             "subnet": "10.0.0.0/24",
             "pools": [
               {
                 "pool": "10.0.0.200 - 10.0.0.250"
               }
             ],
             "option-data": [
               {
                 "name": "routers",
                 "data": "10.0.0.1"
               },
               {
                 "name": "domain-name-servers",
                 "data": "10.0.0.2, 10.0.0.3"
               }
             ]
           }
         ]
       }
     ],
     "host-reservation-identifiers": [
       "hw-address"
     ],
     "reservation-mode": "global",
     "reservations": [
       {
         "hw-address": "aa:a0:00:00:11:10",
         "ip-address": "10.0.0.9",
         "hostname": "client-X"
       }
     ]
   }
}

---

dhclient-debug.sh:

#!/bin/sh
env

---

ip add
...
     link/ether aa:a0:00:00:11:10 brd ff:ff:ff:ff:ff:ff link-netnsid 1
...


dhclient client1-eth0 --timeout 2 -sf dhclient-debug.sh -H client-X
...
new_ip_address=10.0.0.9
new_routers=10.1.1.1
new_domain_name_servers=10.1.1.2 10.1.1.3
...